Determination of sodium chloride in sodium hypochlorite | Autotitrator

HIRANUMA APPLICATION DATA

Automatic Titrator

Data No.

Apr. 5,2019

SODA PULP INDUSTRY

Determination of sodium chloride in sodium hypochlorite

1. Abstract

Sodium hypochlorite is produced by having sodium hydroxide absorb chlorine gas. Produced sodium hypochlorite contains residual alkali (sodium hydroxide, sodium carbonate) and sodium chloride generated by the degradation of hypochlorous acid. The residual alkali is determined by neutralization titration, and sodium chloride is determined by precipitation titration.

This report introduces an example of the determination for sodium chloride in the sodium hypochlorite with potentiometric titration as the following procedure: the titration for the total chlorine component (sodium hypochlorite + sodium chloride) is performed first. After that, sodium hypochlorite (available chlorine) is titrated by another method. Finally, sodium chloride is determined by the subtraction of sodium hypochlorite from the total chloride component.

The total sodium chloride (total chloride component) is determined according to the following formula (1) and (2): add hydrogen peroxide into a sample to degrade sodium hypochlorite, and generate sodium chloride as described in formula (1). Titrate with nitric acid standard solution until the pH goes down to 2 ~ 3. After the solution is acidified, determine the total sodium chloride with silver nitrate standard solution by precipitation titration as formula (2).

NaClO + H₂O₂ → NaCl + H₂O + O₂	・・・(1)
NaCl + AgNO₃ → AgCl + NaNO₃	・・・(2)

Regarding the determination of available chlorine, free iodine generated by the addition of potassium iodide as described in formula (3) is determined with sodium thiosulfate standard solution by redox titration as shown in formula (4).

NaClO + 2KI ± H₂O → I₂ + NaCl + 2KOH	・・・(3)
I₂ + 2Na₂S₂O₃ → 2NaI + Na₂S₄O₆	・・・(4)

2. Configuration of instruments and Reagents

(1)	Configuration of instruments
	Main unit	:	Hiranuma Automatic Titrator COM series
	Option	:	One buret, one buret head
	Electrodes	:	[For total sodium chloride] Glass electrode GE-101B Silver combination electrode AGR-811Z (Double junction type) [For available chlorine] Platinum electrode PT-301 Reference electrode RE-201Z
(2)	Reagents
	[For total sodium chloride]
	Titrant	:	0.2 mol/L Silver nitrate standard solution 0.1 mol/L Nitric acid standard solution
	Additive	:	3 % Hydrogen peroxide solution
	[For available chlorine]
	Titrant	:	0.2 mol/L Sodium thiosulfate standard solution
	Additive	:	10 % Potassium iodide solution 2 mol/L Acetic acid solution

3. Measurement procedure

(1)

Measurement for total sodium chloride
(i) Dispense 0.5 mL of sample into a 100 mL beaker with micropipette.
(ii) Add 50 mL of DI water.
(iii) Add 5 mL of 3 % hydrogen peroxide solution and degrade sodium hypochlorite.
(iv) Immerse the electrodes (GE-101B/AGR-811Z) into sample solution.
Titrate with 0.1 mol/L nitric acid standard solution and adjust the pH to 2 ~ 3.
(v) Titrate with 0.2 mol/L silver nitrate standard solution.

(2)

Measurement for available chlorine
(i) Dispense 0.5 mL of sample into a 100 mL beaker with micropipette.
(ii) Add 50 mL of DI water.
(iii) Add 1 mL of 10 % potassium iodide solution.
(iv) Add 10 mL of 2 mol/L acetic acid solution.
(v) Immerse electrodes (PT-301/RE-201Z) and titrate with 0.2 mol/L sodium thiosulfate standard solution.

4. Measurement conditions and results

Examples of titration conditions

(1) Measurement for total sodium chloride
(i) Titration with 0.1 mol/L nitric acid standard solution

Cndt No	1
Method	Set
Buret No.	1
Amp No.	1
D. Unit	pH
S-Timer	5	sec
C.P. mL	0	mL
Direction	↓
T Timer	0	sec
D.P. mL	0	mL
End Point	3	pH
Over mL	0	mL
Max Vol.	20	mL

Constant No.	1
Size	0.5	mL
Blank	0	mL
Molarity	0.1	mol/L
Factor	1.004
K	0
L	0

Unit	mL
Formula	D
Decimal Places	3
Auto In Pram.		None

Mode No.	4
Pre Int	0	sec
Del K	9
Del Sens	0	mV
Int Time	3	sec
Int Sens	3	mV
Brt Speed	2
Pulse	40

(ii) Titration with 0.2 mol/L silver nitrate standard solution

Cndt No	2
Method	Auto
Buret No.	2
Amp No.	2
D. Unit	mV
S-Timer	5	sec
C.P. mL	0	mL
T Timer	0	sec
D.P. mL	0	mL
End Sens	100
Over mL	0.2	mL
Max Vol.	20	mL

Constant No.	2
Size	0.5	mL
Blank	0	mL
Molarity	0.2	mol/L
Factor	1
K	58.44
L	0

Unit	%
Formula	(D-B)KFM/(S10)
Decimal Places	4
Auto In Pram.		None

Mode No.	8
Pre Int	0	sec
Del K	5
Del Sens	0	mV
Int Time	5	sec
Int Sens	3	mV
Brt Speed	2
Pulse	40

(2) Measurement for available chlorine (Calculation of sodium chloride concentration)
(i)Titration with 0.2 mol/L sodium thiosulfate standard solution

Cndt No.	3
Method	Auto
Buret No.	1
Amp No.	2
D. Unit	mV
S-Timer	5	sec
C.P. pH	0	mL
T Timer	0	sec
D.P. mL	0	mL
End Sens	200
Over mL	0.3	mL
Max Vol.	20	mL

ConstantNo.	3
Size	0.5	mL
Blank	0	mL
Molarity	0.2	mol/L
Factor	1.002
K	35.45
L	0

Unit	%
Formula	(D-B)KFM/(S10)
Decimal Places	4
Auto In Pram.		None

Mode No.	5
Pre Int	0	sec
Del K	5
Del Sens	0	mV
Int time	3	sec
Int Sens	3	mV
Brt Speed	2
Pulse	40

(ii) Calculation of sodium chloride concentration

Cndt No.	4
Method	Calc

ConstantNo.	4
Size	0.5	mL
Blank	0	mL
Molarity	0.2	mol/L
Factor	0
K	14.8	*1
L	0.8243	*2

Unit	%
Formula	K-CA*L
Decimal Places	4
Auto In Pram.		None

*1 Input the result of total sodium chloride.

*2 Conversion coefficient from available chlorine to sodium chloride (58.44(NaCl)/70.9(Cl2))

Measurement results

(1) Results of total sodium chloride

Number of measurement	Size (mL)	Titrant Volume(mL)	Total sodium chloride Concentration (%)
1	0.5	6.329	14.795
2	0.5	6.324	14.783
3	0.5	6.339	14.818
Statistic calculation	Avg.		14.80 %
	SD		0.02 %
	RSD		0.12 %

(2) Results of available chlorine (Calculated results of sodium chloride concentration)

Number of measurement	Size (mL)	Titrant volume (mL)	Available chlorine Concentration (%)	Sodium chloride Concentration (%)
1	0.5	10.174	14.456	2.884
2	0.5	10.223	14.525	2.827
3	0.5	10.276	14.601	2.765
Statistic calculation	Average		14.52 %	2.83 %
	Standard deviation		0.07 %	0.06 %
	Coefficient of variation		0.50 %	2.11 %